Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming, and ultimately very expensive endeavors. As a result, over the years, a tremendous amount of added emphasis has been placed on monitoring and maintaining wells throughout their productive lives. Well monitoring and maintenance may be directed at maximizing production as well as extending well life. In the case of well monitoring, logging and other applications may be utilized which provide temperature, pressure and other production related information. In the case of well maintenance, a host of interventional applications may come into play. For example, perforations may be induced in the wall of the well, regions of the well closed off, debris or tools and equipment removed that have become stuck downhole, etc. Additionally, in some cases, locations in the well may be enhanced, repaired or otherwise treated by the introduction of downhole treatment fluids such as those containing acid jetting constituents, flowback control fibers and others.
With respect to the delivery of downhole treatment fluid, several thousand feet of coiled tubing may be advanced through the well until a treatment location is reached. In man cases a variety of treatment locations may be present in the well, for example, where the well is of multilateral architecture. Regardless, the advancement of the coiled tubing to any of the treatment locations is achieved by appropriate positioning of a coiled tubing reel near the well, for example with a coiled tubing truck and delivery equipment. The coiled tubing may then be driven to the treatment location.
Once positioned for treatment, a valve assembly at the end of the coiled tubing may be opened and the appropriate treatment fluid delivered. For example, the coiled tubing may be employed to locate and advance to within a given lateral leg of the well for treatment therein. As such, a ball, dart, or other projectile may be dropped within the coiled tubing for ballistic actuation and opening of the valve at the end of the coiled tubing. Thus, the treatment fluid may be delivered to the desired location as indicated. So, by way of example, an acid jetting clean-out application may take place within the targeted location of the lateral leg.
Unfortunately, once a treatment application through a valve assembly is actuated as noted above, the entire coiled tubing has to be removed from the well to perform a subsequent treatment through the assembly. That is, as a practical matter, in order to re-close the valve until the next treatment location is reached for a subsequent application, the valve should be manually accessible. In other words, such treatments are generally ‘single-shot’ in nature. For example, once a ball is dropped to force open a sleeve or other port actuating feature, the port will remain open until the ball is manually removed and the sleeve re-closed.
As a result of having to manually access the valve assembly between downhole coiled tubing treatments, a tremendous amount of delay and expense are added to operations wherever multiple coiled tubing treatments are sought. This may be particularly the case where treatments within multilaterals are sought. For example, an acid jetting treatment directed at 3-4 different legs of a multilateral well may involve 6-8 different trips into and out of the well in order to service each leg. That is, a trip in, a valve actuation and clean-out, and a trip out for manual resetting of the valve for each treatment. Given the depths involved, this may add days of delay and tens if not hundreds of thousands of dollars in lost time before complete acid treatment and clean-out to each leg is achieved.
A variety of efforts have been undertaken to address the costly well trip redundancy involved in coiled tubing fluid treatments as noted above. For example, balls or other projectiles utilized for valve actuation may be constructed of degradable materials. Thus, in theory, the ball may serve to temporarily provide valve actuation, thereby obviating the need to remove the coiled tubing in order to reset or re-close the valve. Unfortunately, this involves reliance on a largely unpredictable and uncontrollable rate of degradation. As such, tight controls over the delivery of the treatment fluids or precisely when the coiled tubing might be moved to the next treatment location are foregone.
As an alternative to ball-drop type of actuations, a valve assembly may be utilized which is actuated at given pre-determined flow rates. So, for example, when more than 1 barrel per minute (BPM) is driven through the coiled tubing, the valve may be opened. Of course, this narrows the range of flow rate which may be utilized for the given treatment application and reduces the number of flow rates left available for other applications. In a more specific example, this limits the range of flow available for acid jetting at the treatment location and also reduces flow options available for utilizing flow driven coiled tubing tools, as may be the case for milling, mud motors, or locating tools. Thus, as a practical matter, operators are generally left with the more viable but costly manual retrieval between each treatment.